The invention relates generally to ultrasonic immersion testing of industrial components and, more particularly, to reducing unattenuated sound in a coupling medium to increase testing speed in an ultrasonic immersion inspection.
Ultrasonic testing is a desirable inspection technique for industrial components. However, conventional ultrasonic immersion inspection techniques have limited throughput as a result of the unattenuated sound that reverberates in the coupling medium that is being used to couple ultrasonic energy to the component under test. FIG. 1 depicts a conventional A-scan (amplitude vs. time) display for an ultrasonic immersion test. As indicated in FIG. 1, a number of echoes occur beyond the testing region, which are caused by unattenuated sound. Consequently, conventional immersion ultrasonic scans require relatively long intervals between ultrasonic pulses, in order to permit the echos to decay before the subsequent ultrasonic pulse. FIG. 2 shows a conventional A-scan display for an ultrasonic immersion test where the second ultrasonic pulse occurs before the echo from the first ultrasonic pulse has decayed to an acceptable level. As indicated in FIG. 2, the echo impairs the accuracy with which a flaw can be detected. Because there is generally no method to distinguish between an echo caused by a defect within the test object or an echo caused by unattenuated sound, the presence of an echo caused by unattenuated sound will be interpreted as a defect, resulting in a false positive. The phenomenon of echoes associated with unattenuated sound is generally termed “wraparound” or “ghosting.” To reduce the noise associated with the unattenuated sound, conventional ultrasonic immersion tests are run at relatively low pulse repletion frequencies (prf), for example at five hundred pulses per second (500 pulses/s). Due to the low prfs that must be employed, inspection of a typical aircraft engine component may take on the order of four hours using conventional techniques.
It would therefore be desirable to reduce the unattenuated sound for ultrasonic immersion testing. It would further be desirable to reduce the time necessary to inspect industrial components using ultrasonic immersion inspection techniques.